Generally, a mobile terminal must be subjected to radio frequency calibration before leaving the manufacturer, wherein the radio frequency calibration includes calibration of a radio frequency transmitter. In the related art, the radio frequency transmitter is located in the mobile terminal, and during the calibration performed via the radio frequency transmitter, a calibration program in a Personnel Computer (PC) transmits a power control signal, which can be represented by a PPDM value, to the radio frequency transmitter in the mobile terminal through a Universal Serial Bus (USB) or other serial ports, so as to control power of a radio frequency signal transmitted from the radio frequency transmitter. The radio frequency signal from the radio frequency transmitter is transmitted to an integrated tester through a radio frequency coaxial line. The calibration program controls the integrated tester to measure and acquire a precise power value of the radio frequency signal, and then the calibration program gradually increases or decreases the PPDM value according to a certain step, and synchronously measures the power of the radio frequency signal transmitted from the radio frequency transmitter to finally obtain a series of power values corresponding to the PPDM values.
Because a linear Power Amplifier (PA) adopted by the mobile terminal is characterized by multi-level gain, the scanning calibration process above will be performed in stages. Specifically, if the gain of the PA is of N levels, the PPDM scanning range corresponding to the gain of each level is: (PPDM[0](start)˜PPDM[0](stop)), (PPDM[1](start)˜PPDM[1](stop)), . . . , (PPDM[N-1](start)˜PPDM[N-1](stop)), wherein N is an integer more than or equal to 1, the output power of the radio frequency transmitter corresponding to the PPDM start and stop values would be better to cover a dynamic range of the gain of the level, the PPDM scanning range of each stage corresponds to one PPDM scanning step length (also referred to as step), here, step is an integer more than or equal to 1, and scanning is performed in stages according to the gain levels of the PA so as to finally measure and obtain the power values in stages.
The series of power values obtained by calibration are converted into data recognizable by the mobile terminal in a scale conversion way, wherein the data recognizable by the mobile terminal can be represented by PAGC value. The PAGC value is stored into a pre-allocated mobile terminal memory with a fixed length for the gain of each level. Meanwhile, the PPDM value corresponding to the PAGC value is also stored into the mobile terminal memory. In this way, the mobile terminal memory has a table of correspondence between each gain level working mode of the PA and the corresponding output power of the transmitter, and this table is generally referred to as a linear table, including a series of corresponding relationships between the PPDM value and the PAGC value. When transmitting power to the outside, the mobile terminal queries the linear table to transmit the correct power. The shorter the scanning step of the PPDM in the calibration is, the finer the obtained linear table is, and the more accurate the power from the mobile terminal is. The power range of the linear table is required to cover the dynamic range of the normal working output power of the mobile terminal.
Based on what described above, the radio frequency calibration method for the transmitter in the related art mainly includes the following steps.
Step 101: Radio frequency calibration related parameters are set.
In the step, it is required to set a PA gain level (N), a mode of the gain of each level (R[i]), PPDM scanning start-stop range (PPDM (start), PPDM (stop)) corresponding to the gain of each level, and PPDM scanning step (Step [i]) corresponding to the gain of each level, wherein the PPDM scanning start-stop range corresponding to the gain of each level may be specifically set with reference to documents related to a platform solution of the mobile terminal, platform solutions of different manufactures correspond to different PPDM scanning start-stop ranges, and the scanning step corresponding to the gain of each level may also be different, wherein N is a natural number and i represents different gain levels, i=0, 1, 2 . . . N−1.
Step 102: The gain mode of the PA is set and the PPDM scanning start-stop range corresponding to the gain of each level is obtained.
Step 103: A PPDM value is transmitted to the mobile terminal by a calibration program to make the mobile terminal transmit a radio frequency signal to the outside, and the calibration program controls an integrated tester to measure and obtain the power P of the signal transmitted by the mobile terminal.
Step 104: It is judged whether the PPDM scanning range of the current gain ends, if not, Step 105 is executed; otherwise, Step 106 is executed.
Step 105: A next PPDM value is set according to the PPDM scanning step of the current gain, and return to Step 103.
Step 106: It is judged whether the calibration of the gains of N levels has been completed, if not, Step 107 is executed; otherwise, Step 108 is executed.
Step 107: The calibration of the gain of the next level is performed and Step 102 is circularly executed.
Step 108: The measured power (P) of each stage is converted into a PAGC value recognizable by the mobile terminal. The PAGC value is assigned to an array (Master), and written into a memory specified by the mobile terminal. Meanwhile, the PPDM value corresponding to the PAGC value is written into a memory specified by the mobile terminal in the form of an array.
In the related art, the mobile terminal has a memory space of fixed length, so the PPDM array and the Master array written into the memory of the mobile terminal are fixed in size. One of the following three circumstances would occur when the size L of the PPDM array and the Master array finally obtained by calibration in accordance with the above method is compared with the size L′ of the space allocated to store the PPDM data and the Master data in the memory, where L=round ((PPDM(stop)−PPDM(start)/Step).
The first circumstance is L=L′, this is the most ideal circumstance.
The second circumstance is L>L′, the power range of the linear table written into the memory of the mobile terminal cannot cover the dynamic range of the normal working output power of the mobile terminal, as a result, the transmission index of the mobile terminal will be affected.
The third circumstance is L<L′, the PPDM scanning is not fine and the memory space of the mobile terminal is not used up, under such circumstance, the transmission index of the mobile terminal will not be affected if the linearity of the PA or the radio frequency transmission of the mobile terminal is excellent, and will be affected if the linearity is not good.
Generally, the second circumstance may be solved by increasing the step, and the third circumstance may be solved by decreasing the step.
However, in actual application, a lot of projects and experiments show that: because the PPDM scanning step of each stage is constant, the final result is either the second circumstance turning into the third circumstance, or the third circumstance turning into the second circumstance no matter how the step is adjusted, and it is almost impossible to achieve the first ideal circumstance. Whereas, under the third circumstance, in one aspect, the calibration scanning is not fine due to the non-ideal linearity of the PA or the non-ideal linearity of the radio frequency transmission of the mobile terminal, as a result, the transmission index, particularly an inner-loop power control index, of the mobile terminal is affected; and in another aspect, in actual application, the L is only about ⅔ or ¾ as long as L′, as a result, the memory space of the linear table is wasted.